A large number of RNAs are not diffusely distributed in the cytoplasm, but are actively transported to various subcellular sites. After reaching their final destinations, localized RNAs are translated, thus directing local protein production. While increasing numbers of localized RNAs are being identified, the functional importance of these events, as well as the overall applicability of the above model, is not well understood. We are focusing on a localization pathway that we have identified, which targets a number of RNAs to cellular protrusions. This pathway is of interest because it targets RNAs encoding factors that have been implicated in progression of various types of cancers. Furthermore, as we have found, it is regulated by disease-associated proteins, such as APC (Adenomatous Polyposis Coli), a tumor-suppressor protein whose loss underlies the initiation of most colorectal tumors, as well as by the RNA-binding protein FUS, a protein mutated in cases of Amyotrophic Lateral Sclerosis. Our overall goals have been to: a) understand the basic mechanisms underlying localization of RNAs at cell protrusions, b) understand the functional outcomes of their localization, either as a group or at the level of individual transcripts and c) set up appropriate model systems and tools to study RNA localization events in physiologically and pathologically relevant settings. With regards to the underlying mechanisms, we have revealed that localization of RNAs at protrusions requires a specific subset of modified microtubules in a process that is disrupted by pathologic inclusions associated with neurodegeneration. We have further shown that RNA localization at protrusions is modulated by the mechanical properties of the extracellular environment and have probed into the molecular basis of this phenomenon. Finally, we have made the intriguing discovery that, contrary to the prevailing model, translation of protrusion-localized RNAs is not affected by their position in the cytoplasm, but is rather coordinated with specific peripheral cellular processes, being activated at extending protrusions and silenced upon protrusion retraction. This coordination is dynamic and is coupled to a change in the physical state of the RNA. With regards to the functional roles of protrusion-localized RNAs, we have shown that their localization is important for efficient cell migration. We have devised ways to disrupt localization of specific, individual RNAs and have shown that disrupting the localization of just one RNA is sufficient to cause significant migration defects in 2D and 3D systems, as well as to reduce collective invasion of cancer cells. We are optimizing our current approaches for in vivo delivery to further test the roles of protrusion-localized RNAs in animal models of tumor metastasis. Apart from migrating cells, our recent studies have revealed that APC-dependent RNAs are also localized in non-invasive, epithelial cells, where they are concentrated at the basal surface. A separate line of investigation is thus exploring the functional roles of basally localized APC-dependent RNAs in 2D or 3D epithelial systems. Given the role of APC as an initiator of tumorigenesis in the intestinal epithelium, we believe these studies might reveal roles of localized RNAs relevant to the initial stages of tumor formation.